This invention relates to thermally-developable imaging materials such as photothermographic materials that exhibit high speed imaging characteristics. In particular, this invention relates to the use of certain selenium compounds as chemical sensitizers in photothermographic materials to provide increased photothermographic speed. This invention also relates to methods of imaging using these photothermographic materials.
Silver-containing photothermographic imaging materials that are developed with heat and without liquid development have been known in the art for many years. Such materials are used in a recording process wherein an image is formed by imagewise exposure of the photothermographic material to specific electromagnetic radiation (for example, visible, ultraviolet, or infrared radiation) and developed by the use of thermal energy. These materials, also known as xe2x80x9cdry silverxe2x80x9d materials, generally comprise a support having coated thereon: (a) a photocatalyst (that is, a photosensitive compound such as a silver halide) that upon such exposure provides a latent image in exposed grains that is capable of acting as a catalyst for the subsequent formation of a silver image in a development step, (b) a non-photosensitive source of reducible silver ions, (c) a reducing composition (usually including a developer) for the reducible silver ions, and (d) a hydrophilic or hydrophobic binder. The latent image is then developed by application of thermal energy.
In such materials, the photosensitive catalyst is generally a photographic type photosensitive silver halide that is considered to be in catalytic proximity to the non-photosensitive source of reducible silver ions. Catalytic proximity requires intimate physical association of these two components, either prior to or during the thermal image development process, so that when silver atoms (Ag0)n, also known as silver specks, clusters, nuclei or latent image, are generated by irradiation or light exposure of the photosensitive silver halide, those silver atoms are able to catalyze the reduction of the reducible silver ions within a catalytic sphere of influence around the silver atoms [D. H. Klosterboer, Imaging Processes and Materials, (Neblette""Eighth Edition), J. Sturge, V. Walworth, and A. Shepp, Eds., Van Nostrand-Reinhold, New York, 1989, Chapter 9, pp. 279-291]. It has long been understood that silver atoms act as a catalyst for the reduction of silver ions, and that the photosensitive silver halide can be placed in catalytic proximity with the non-photosensitive source of reducible silver ions in a number of different ways (see, for example, Research Disclosure, June 1978, item 17029). Other photosensitive materials, such as titanium dioxide, cadmium sulfide, and zinc oxide have also been reported to be useful in place of silver halide as the photocatalyst in photothermographic materials [see, for example, Shepard, J. Appl. Photog. Eng. 1982, 8(5), 210-212, Shigeo et al., Nippon Kagaku Kaishi, 1994, 11, 992-997, and FR 2,254,047 (Robillard)].
The photosensitive silver halide may be made xe2x80x9cin-situ,xe2x80x9d for example by mixing an organic or inorganic halide-containing source with a source of reducible silver ions to achieve partial metathesis and thus causing the in-situ formation of silver halide (AgX) grains throughout the silver source [see, for example, U.S. Pat. No. 3,457,075 (Morgan et al.)]. In addition, photosensitive silver halides and sources of reducible silver ions can be co-precipitated [see Yu. E. Usanov et al., J. Imag. Sci. Tech. 1996, 40, 104]. Alternatively, a portion of the reducible silver ions can be completely converted to silver halide, and that portion can be added back to the source of reducible silver ions (see Yu. E. Usanov et al., International Conference on Imaging Science, Sep. 7-11, 1998).
The silver halide may also be xe2x80x9cpreformedxe2x80x9d and prepared by an xe2x80x9cex-situxe2x80x9d process whereby the silver halide (AgX) grains are prepared and grown separately. With this technique, one has the possibility of controlling the grain size, grain size distribution, dopant levels, and composition much more precisely, so that one can impart more specific properties to both the silver halide grains and the photothermographic material. The preformed silver halide grains may be introduced prior to, and be present during, the formation of the source of reducible silver ions. Co-precipitation of the silver halide and the source of reducible silver ions provides a more intimate mixture of the two materials [see, for example, U.S. Pat. No. 3,839,049 (Simons)]. Alternatively, the preformed silver halide grains may be added to and physically mixed with the source of reducible silver ions.
The non-photosensitive source of reducible silver ions is a material that contains reducible silver ions. Typically, the preferred non-photosensitive source of reducible silver ions is a silver salt of a long chain aliphatic carboxylic acid having from 10 to 30 carbon atoms, or mixtures of such salts. Such acids are also known as xe2x80x9cfatty acidsxe2x80x9d or xe2x80x9cfatty carboxylic acidsxe2x80x9d. Silver salts of other organic acids or other organic compounds, such as silver imidazoles, silver tetrazoles, silver benzotriazoles, silver benzotetrazoles, silver benzothiazoles and silver acetylides have also been used. U.S. Pat. No. 4,260,677 (Winslow et al.) discloses the use of complexes of various inorganic or organic silver salts.
In photothermographic materials, exposure of the photographic silver halide to light produces small clusters containing silver atoms (Ag0)n. The imagewise distribution of these clusters, known in the art as a latent image, is generally not visible by ordinary means. Thus, the photosensitive material must be further developed to produce a visible image. This is accomplished by the reduction of silver ions that are in catalytic proximity to silver halide grains bearing the silver-containing clusters of the latent image. This produces a black-and-white image. The non-photosensitive silver source in the exposed areas is catalytically reduced to form the visible black-and-white negative image while the silver halide and the non-photosensitive silver source in the unexposed areas are not reduced.
In photothermographic materials, the reducing agent for the reducible silver ions, often referred to as a xe2x80x9cdeveloper,xe2x80x9d may be any compound that, in the presence of the latent image, can reduce silver ion to metallic silver and is preferably of relatively low activity until it is heated to a temperature sufficient to cause the reaction. A wide variety of classes of compounds have been disclosed in the literature that function as developers for photothermographic materials. At elevated temperatures, the reducible silver ions are reduced by the reducing agent. In photothermographic materials, upon heating, this reaction occurs preferentially in the regions surrounding the latent image. This reaction produces a negative image of metallic silver having a color that ranges from yellow to deep black depending upon the presence of toning agents and other components in the imaging layer(s).
The imaging arts have long recognized that the field of photothermography is clearly distinct from that of photography. Photothermographic materials differ significantly from conventional silver halide photographic materials that require processing with aqueous processing solutions.
As noted above, in photothermographic imaging materials, a visible image is created by heat as a result of the reaction of a developer incorporated within the material. Heating at 50xc2x0 C. or more is essential for this dry development. In contrast, conventional photographic imaging materials require processing in aqueous processing baths at more moderate temperatures (from 30xc2x0 C. to 50xc2x0 C.) to provide a visible image.
In photothermographic materials, only a small amount of silver halide is used to capture light and a non-photosensitive source of reducible silver ions (for example a silver carboxylate) is used to generate the visible image using thermal development. Thus, the imaged photosensitive silver halide serves as a catalyst for the physical development process involving the non-photosensitive source of reducible silver ions and the incorporated reducing agent. In contrast, conventional wet-processed, black-and-white photographic materials use only one form of silver (that is, silver halide) that, upon chemical development, is itself at least partially converted into the silver image, or that upon physical development requires addition of an external silver source (or other reducible metal ions that form black images upon reduction to the corresponding metal). Thus, photothermographic materials require an amount of silver halide per unit area that is only a fraction of that used in conventional wet-processed photographic materials.
In photothermographic materials, all of the xe2x80x9cchemistryxe2x80x9d for imaging is incorporated within the material itself. For example, such materials include a developer (that is, a reducing agent for the reducible silver ions) while conventional photographic materials usually do not. Even in so-called xe2x80x9cinstant photography,xe2x80x9d the developer chemistry is physically separated from the photosensitive silver halide until development is desired. The incorporation of the developer into photothermographic materials can lead to increased formation of various types of xe2x80x9cfogxe2x80x9d or other undesirable sensitometric side effects. Therefore, much effort has gone into the preparation and manufacture of photothermographic materials to minimize these problems during the preparation of the photothermographic emulsion as well as during coating, use, storage, and post-processing handling.
Moreover, in photothermographic materials, the unexposed silver halide generally remains intact after development and the material must be stabilized against further imaging and development. In contrast, silver halide is removed from conventional photographic materials after solution development to prevent further imaging (that is, in the aqueous fixing step).
In photothermographic materials, the binder is capable of wide variation and a number of binders (both hydrophilic and hydrophobic) are useful. In contrast, conventional photographic materials are limited almost exclusively to hydrophilic colloidal binders such as gelatin.
Because photothermographic materials require dry thermal processing, they present distinctly different problems and require different materials in manufacture and use, compared to conventional, wet-processed silver halide photographic materials. Additives that have one effect in conventional silver halide photographic materials may behave quite differently when incorporated in photothermographic materials where the chemistry is significantly more complex. The incorporation of such additives as, for example, stabilizers, antifoggants, speed enhancers, supersensitizers, and spectral and chemical sensitizers in conventional photographic materials is not predictive of whether such additives will prove beneficial or detrimental in photothermographic materials. For example, it is not uncommon for a photographic antifoggant useful in conventional photographic materials to cause various types of fog when incorporated in photothermographic materials, or for supersensitizers that are. effective in photographic materials to be inactive in photothermographic materials.
These and other distinctions between photothermographic and photographic materials are described in Imaging Processes and Materials (Neblette""Eighth Edition), noted above, Unconventional Imaging Processes, E. Brinckman et al. (Eds.), The Focal Press, London and New York, 1978, pp. 74-75, in C. Zou et al., J. Imaging Sci. Technol. 1996, 40, pp. 94-103, and in M. R. V. Sahyun, J. Imaging Sci. Technol. 1998, 42, 23.
One of the challenges in the use of photothermographic materials is attaining sufficient photothermographic speed in such materials to permit the use of conventional imaging sources.
Each of the pure photographic silver halides (silver chloride, silver bromide and silver iodide) has its own natural response to radiation, in both wavelength and speed, within the UV, near UV and blue regions of the electromagnetic spectrum. Mixtures of silver halides (for example, silver bromochloroiodide, silver chloroiodide, silver chlorobromide and silver iodobromide) also have their own natural sensitivities within the UV and blue regions of the electromagnetic spectrum. Thus, silver halide grains, when composed of only silver and halogen atoms have defined levels of sensitivity depending upon the levels of specific halogen, crystal morphology (shape and structure of the crystals or grains) and other characteristics such as, for example, crystal defects, stresses, and dislocations, and dopants incorporated within or on the crystal lattice of the silver halide. These features may or may not have been controlled or purposely introduced to affect emulsion sensitometry.
The efforts to influence silver halide grain speed in conventional wet-processed silver halide emulsions generally fall within the investigation of crystal composition, morphology or structure (all briefly described above), or the use of dopants, spectral sensitizers, supersensitizers, reduction sensitizers, and chemical sensitizers (including sulfur, tellurium, and selenium sensitizers).
Spectral sensitization is the addition of a compound (usually a dye) to silver halide grains that absorbs radiation at wavelengths (UV, visible or IR) other than those to which the silver halide is naturally sensitive, or that absorbs radiation more efficiently than silver halide (even within the regions of silver halide""natural sensitivity). It is generally recognized that spectral sensitizers extend the responses of photosensitive silver halide to longer wavelengths. After absorption of the radiation, these compounds transfer energy or electrons to the silver halide grains to cause the necessary local photoinduced reduction of silver(I) to silver(0).
Supersensitization is a process whereby the speed of spectrally sensitized silver halide is increased by the addition of still another compound that may or may not be a dye. This is not merely an additive effect of the two compounds (spectral sensitizer and supersensitizer).
Reduction sensitization is a type of chemical sensitization (described in more detail in the following paragraphs) in which other chemical species (not sulfur-containing) are deposited onto, or reacted with, the silver halide grains during grain growth and finishing. Compounds used for this purpose act as reducing agents on the silver halide grains and include, but are not limited to, stannous chloride, hydrazine, ethanolamine, and thiourea oxide.
Chemical sensitization (generally sulfur and/or gold sensitization) is a process, during or after silver halide crystal formation, in which sensitization centers [for example, silver sulfide clusters such as (Ag2S)n] are introduced onto the individual silver halide grains. For example, silver sulfide specks can be introduced by direct reaction of sulfur-contributing compounds with the silver halide during various stages, or after completion, of silver halide grain growth. These specks usually function as shallow electron traps for the preferential formation of latent image centers. Other chalcogens (Se and Te) can function similarly. The presence of these specks increases the speed or sensitivity of the resulting silver halide grains to radiation. Sulfur-contributing compounds useful for this purpose include thiosulfates (such as sodium thiosulfate) and various thioureas (such as allyl thiourea, thiourea, triethyl thiourea and 1,1xe2x80x2-diphenyl-2-thiourea) as described for example, by Sheppard et al., J. Franklin Inst., 1923, 196, 653 and 673, C. E. K. Mees and T. H. James, The Theory of the Photographic Process, Fourth Edition, Eastman Kodak Company, Rochester, N.Y., 1977, pp. 152-3, and T. Tani, Photographic Sensitivity. Theory and Mechanisms, Oxford University Press, NY, 1995, pp. 167-176.
Another useful class of chemical sensitizers includes tetrasubstituted thioureas as described in copending and commonly assigned U.S. Ser. No. 09/667,748 (filed Sep. 21, 2000 by Lynch, Simpson, Shor, Willett, and Zou). These compounds are thioureas in which the nitrogen atoms are fully substituted with various substituents.
Still another method of chemical sensitization is achieved by oxidative decomposition of a sulfur-containing spectral sensitizing dye in a photothermographic emulsion as described in U.S. Pat. No. 5,891,615 (Winslow et al.).
Chemical sensitization to increase photospeed has also been achieved by treating the silver halide grains with gold-containing ions such as tetrachloroaurate(3+), dithiocyanatoaurate(1+) or covalent gold(1+) compounds such as [AuS2P(i-C4H9)2]2. Preferably, the gold compounds are added in the later stages of silver halide grain formation such as during ripening. Platinum and palladium compounds are also known to have similar effects. In comparison, iridium, rhodium, and ruthenium compounds are generally used to control contrast and/or high intensity reciprocity effects rather than to increase speed. It is well known that the various speed enhancing means just described can be used in combination as the situation requires.
As noted above, in photothermographic emulsions, the photosensitive silver halide must be in catalytic proximity to the non-photosensitive source of reducible silver ions. Because of the different emulsion making procedures and chemical environments of photothermographic emulsions, the effects achieved by compounds (such as chemical sensitizers) in conventional photographic emulsions are not necessarily possible in photothermographic emulsions.
For example, in photothermographic emulsions, two types of chemical sensitization have been used to increase speed: (a) chemical sensitization of preformed silver halide grains that are then mixed into the solution or dispersion containing reducible silver ions in some manner, and (b) chemical sensitization of preformed silver halide grains that are already in intimate contact with the reducible silver ions.
In the first approach (a), many of the traditional methods (used for photographic emulsions) can be used, but for the second approach (b), quite specific methods and unique compounds are often needed. Regardless of which approach is used, there is considerable difficulty in attaining additional speed while maintaining low fog (Dmin).
Selenium chemical sensitization of photothermographic materials has been reported. For example, U.S. Pat. No. 4,036,650 (Hasegawa et al.) describes the use of various metallized organosulfur compounds, including certain organosulfur selenides, as chemical sensitizers in heat-developable imaging materials. Other conventional chalcogen chemical sensitizing compounds, including selenium compounds, are described similarly in various patents including U.S. Pat. No. 5,998,127 (Toya et al.), U.S. Pat. No. 6,110,659 (Hatakeyama et al.), U.S. Pat. No. 6,100,022 (Inoue et al.), U.S. Pat. No. 6,083,681 (Lynch et al.), U.S. Pat. No. 6,083,080 (Ito et al.), and U.S. Pat. No. 6,040,131 (Eshelman et al.).
Photothermographic materials are constantly being redesigned to meet ever-increasing performance, storage, and manufacturing demands raised by customers, regulators, and manufacturers. One of these demands is increased photospeed without a significant increase in fog (Dmin) or a loss in maximum image density (Dmax).
The present invention relates to our discovery that the use of certain selenium compounds as chemical sensitizers provides photothermographic materials having increased photospeed without a significant increase in Dmin 
The present invention provides the desired benefits with a photothermographic material comprising a support having thereon one or more layers comprising a binder and in reactive association:
a. a preformed photosensitive silver halide,
b. a non-photosensitive source of reducible silver ions,
c. a reducing composition for the reducible silver ions, and
d. a selenium chemical sensitizer represented by the following Structures I, II, or III:
Se(L)m(X1)nxe2x80x83xe2x80x83(I)
M(Lxe2x80x2)s(X2)rxe2x80x83xe2x80x83(II)
(Z)wMxe2x80x2xSey(CO)zxe2x80x83xe2x80x83(III)
xe2x80x83wherein X1 and X2 independently represent halo, CN, SCN, SeCN, TeCN, N3, BF4, ClO4, BPh4, PF6, NO3, SO3CF3, Ra, Rb, O(Cxe2x95x90O)CF3, S(Cxe2x95x90S)N(Ra)(Rb), S(Cxe2x95x90S)ORa, S(Cxe2x95x90S)SRa, S(Pxe2x95x90S)(ORa)(ORb), S(Pxe2x95x90S)(Ra)(Rb), SRa, SeRa, TeRaORa, or O(Cxe2x95x90O)Ra groups,
Ra and Rb independently represent alkyl, alkenyl, cycloalkyl, heterocyclyl, or aryl groups, or Ra and Rb taken together can form a 5-, 6- or 7-membered heterocyclic ring,
L is a ligand derived from a neutral Lewis base,
m is 0, 1, 2, 3, or 4 and n is 2 or 4 with the proviso that when m is 0, n is 2 or 4, and when m is 0 and n is 2, then X1 is not Ra, Rb, or RaSe,
M represents Cu(1+), Pd(2+), or Pt(2+),
Lxe2x80x2 represents a neutral ligand with a Group 15 atom or a Group 16 atom, provided that at least one of Lxe2x80x2 or X2 contains a selenium atom,
r is 1 or 2 and s is 1, 2, 3, or 4 such that when M represents Cu(1+), r is 1 and when M represents Pd(2+) or Pt(2+), r is 2,
Z represents a monovalent cation,
Mxe2x80x2 represents Fe, Ru, Os, Co, Rh, or Ir,
x is an integer of from 1 to 6, y is an integer of from 1 through 6, z is an integer of from 6 through 20, w is an integer inclusive of from 0 through 4 and represents the number of Z groups necessary to neutralize the electronic charge on the rest of the compound,
and further provided that multiple X1, X2, L, Lxe2x80x2, Ra, Rb, groups in the molecule can be the same or different.
In some Structure I embodiments, when m is 0 and n is 2 or 4 the compounds represented by Structure I can be further represented by Structure I-a, 
wherein X represents the same or different CORa, CSRa, CN(Ra)(Rb), CRa, P(Ra)(Rb), or P(ORa)(ORb) group, Ra and Rb are as defined above, and p is 2 or 4.
In some embodiments, one or more thiourea ligands useful in the selenium compounds (for example, L in Structure I or Lxe2x80x2 in Structure II) are derived from compounds represented by the following Structures IV, V, or VI: 
wherein:
in Structure IV, R1, R2, R3 and R4 are independently hydrogen, alkyl, cycloalkyl, alkenyl, alkynyl, aryl or heterocyclic groups, or R, and R2 taken together, R3 and R4 taken together, R1 and R3 taken together or R2 and R4 taken together, can form a 5- to 7-membered heterocyclic ring, and
in Structure V, R1, R2, R3, R4 and R5 are independently hydrogen, alkyl, cycloalkyl, allyl, alkenyl, alkynyl, aryl or heterocyclic groups, or R3 and R5 taken together, R4 and R5 taken together, R1 and R3 taken together or R2 and R4 taken together, can form a substituted or unsubstituted 5- to 7-membered heterocyclic ring, and
in Structure VI, R1, R2, R3, R4, R5, and R6 are independently hydrogen, alkyl, cycloalkyl, allyl, alkenyl, alkynyl, aryl or heterocyclic groups, or R3 and R6 taken together, R4 and R5 taken together, R1 and R3 taken together, R2 and R4 taken together, or R5 and R6 taken together, can form a substituted or unsubstituted 5- to 7-membered heterocyclic ring, and R7 is a divalent aliphatic or alicyclic linking group.
In further embodiment photothermographic material further comprises a sulfur chemical sensitizer. In one embodiment, the sulfur chemical comprises a thiosulfate, thiazole, rhodanine compound or a thiourea chemical sensitizer represented by Structures IV, V, or VI.
In a still further embodiment, the photothermographic material further comprises tellurium chemical sensitizer.
In yet a still further embodiment, the photothermographic material further comprises gold chemical sensitizer.
Still further chemical sensitization can be achieved by oxidative decomposition of a sulfur-containing compound on or around the silver halide grains in an oxidizing environment.
In a further embodiment photothermographic material further comprises a mixture of two or more of: a sulfur chemical sensitizer, a tellurium chemical sensitizer, a gold chemical sensitizer, or an oxidatively decomposed sulfur-containing compound.
In another embodiment, the present invention provides a photothermographic material comprising a support having thereon one or more layers comprising a binder and in reactive association:
a. a photocatalyst,
b. a non-photosensitive source of reducible silver ions,
c. a reducing composition for the reducible silver ions, and
d. a selenium chemical sensitizer represented by the following Structures I, II, or III:
Se(L)m(X1)nxe2x80x83xe2x80x83(I)
xe2x80x83M(Lxe2x80x2)s(X2)rxe2x80x83xe2x80x83(II)
(Z)wMxe2x80x2xSey(CO)zxe2x80x83xe2x80x83(III)
xe2x80x83wherein X1 and X2 independently represent halo, CN, SCN, SeCN, TeCN, N3, BF4, ClO4, BPh4, PF6, NO3, SO3CF3, Ra, Rb, O(Cxe2x95x90O)CF3, S(Cxe2x95x90S)N(Ra)(Rb), S(Cxe2x95x90S)ORa, S(Cxe2x95x90S)SRa, S(Pxe2x95x90S)(ORa)(ORb), S(Pxe2x95x90S)(Ra)(Rb), SRa, SeRa, TeRa ORa or O(Cxe2x95x90O)Ra groups,
Ra and Rb independently represent alkyl, alkenyl, cycloalkyl, heterocyclyl, or aryl groups, or Ra and Rb taken together can form a 5-, 6- or 7-membered heterocyclic ring,
L is a ligand derived from a neutral Lewis base,
m is 0, 1, 2, 3, or 4 and n is 2 or 4 with the proviso that when m is 0, n is 2 or 4, and when m is 0 and n is 2, then X1 is not Ra, Rb, or RaSe,
M represents Cu(1+), Pd(2+), or Pt(2+),
Lxe2x80x2 represents a neutral ligand with a Group 15 atom or a Group 16 atom, provided that at least one of Lxe2x80x2 or X2 contains a selenium atom,
r is 1 or 2 and s is 1, 2, 3, or 4 such that when M represents Cu(1+), r is 1 and when M represents Pd(2+) or Pt(2+), r is 2,
Z represents a monovalent cation,
Mxe2x80x2 represents Fe, Ru, Os, Co, Rh, or Ir,
x is an integer of from 1 to 6, y is an integer of from 1 through 6, z is an integer of from 6 through 20, w is an integer inclusive of from 0 through 4 and represents the number of Z groups necessary to neutralize the electronic charge on the rest of the compound,
and further provided that multiple X1, X2, L, Lxe2x80x2, Ra, Rb, groups in the molecule can be the same or different.
In some Structure I embodiments, when m is 0 and n is 2 or 4 the compounds represented by Structure I can be further represented by Structure I-a, 
wherein X represents the same or different CORa, CSRa, CN(Ra)(Rb), CRa, P(Ra)(Rb), or P(ORa)(ORb) group, Ra and Rb are as defined above, and p is 2 or 4.
In some embodiments, one or more thiourea ligands useful in the selenium compounds (for example, L in Structure I or Lxe2x80x2 in Structure II) are derived from compounds represented by the following Structures IV, V, or VI: 
wherein:
in Structure IV, R1, R2, R3 and R4 are independently hydrogen, alkyl, cycloalkyl, alkenyl, alkynyl, aryl or heterocyclic groups, or R1 and R2 taken together, R3 and R4 taken together, R1 and R3 taken together or R2 and R4 taken together, can form a 5- to 7-membered heterocyclic ring, and
in Structure V, R1, R2, R3, R4 and R5 are independently hydrogen, alkyl, cycloalkyl, allyl, alkenyl, alkynyl, aryl or heterocyclic groups, or R3 and R5 taken together, R4 and R5 taken together, R1 and R3 taken together or R2 and R4 taken together, can form a substituted or unsubstituted 5- to 7-membered heterocyclic ring, and
in Structure VI, R1, R2, R3, R4, R5, and R6 are independently hydrogen, alkyl, cycloalkyl, allyl, alkenyl, alkynyl, aryl or heterocyclic groups, or R3 and R6 taken together, R4 and R5 taken together, R1 and R3 taken together, R2 and R4 taken together, or R5 and R6 taken together, can form a substituted or unsubstituted 5- to 7-membered heterocyclic ring, and R7 is a divalent aliphatic or alicyclic linking group.
In further embodiment photothermographic material further comprises a sulfur chemical sensitizer. In one embodiment, the sulfur chemical comprises a thiosulfate, thiazole, rhodanine compound or a thiourea chemical sensitizer represented by Structures IV, V, or VI.
In a still further embodiment, the photothermographic material further comprises tellurium chemical sensitizer.
In yet a still further embodiment, the photothermographic material further comprises gold chemical sensitizer.
Still further chemical sensitization can be achieved by oxidative decomposition of a sulfur-containing compound on or around the silver halide grains in an oxidizing environment.
In a further embodiment photothermographic material further comprises a mixture of two or more of: a sulfur chemical sensitizer, a tellurium chemical sensitizer, a gold chemical sensitizer, or an oxidatively decomposed sulfur-containing compound.
This invention also provides a photothermographic material comprising a transparent support having thereon one or more layers one on side thereof comprising a binder and in reactive association:
a. a photocatalyst,
b. a non-photosensitive source of reducible silver ions,
c. a reducing composition for the reducible silver ions, and
d. a selenium chemical sensitizer represented by the following Structures I, II, or III:
Se(L)m(X1)nxe2x80x83xe2x80x83(I)
M(Lxe2x80x2)s(X2)rxe2x80x83xe2x80x83(II)
(Z)wMxe2x80x2xSey(CO)zxe2x80x83xe2x80x83(III)
xe2x80x83wherein X1 and X2 independently represent halo, CN, SCN, SeCN, TeCN, N3, BF4, ClO4, BPh4, PF6, NO3, SO3CF3, Ra, Rb, O(Cxe2x95x90O)CF3, S(Cxe2x95x90S)N(Ra)(Rb), S(Cxe2x95x90S)ORa, S(Cxe2x95x90S)SRa, S(Pxe2x95x90S)(ORa)(ORb), S(Pxe2x95x90S)(Ra)(Rb), SRa, SeRa, TeRaORa, or O(Cxe2x95x90O)Ra groups,
Ra and Rb independently represent alkyl, alkenyl, cycloalkyl, heterocyclyl, or aryl groups, or Ra and Rb taken together can form a 5-, 6- or 7-membered heterocyclic ring,
L is a ligand derived from a neutral Lewis base,
m is 0, 1,2,3, or 4 and n is 2 or 4 with the proviso that when m is 0, n is 2 or 4, and when m is 0 and n is 2, then X1 is not Ra, Rb, or RaSe,
M represents Cu(1+), Pd(2+), or Pt(2+),
Lxe2x80x2 represents a neutral ligand with a Group 15 atom or a Group 16 atom, provided that at least one of Lxe2x80x2 or X2 contains a selenium atom,
r is 1 or 2 and s is 1, 2, 3, or 4 such that when M represents Cu(1+), r is 1 and when M represents Pd(2+) or Pt(2+), r is 2,
Z represents a monovalent cation,
Mxe2x80x2 represents Fe, Ru, Os, Co, Rh, or Ir,
x is an integer of from 1 to 6, y is an integer of from 1 through 6, z is an integer of from 6 through 20, w is an integer inclusive of from 0 through 4 and represents the number of Z groups necessary to neutralize the electronic charge on the rest of the compound,
and further provided that multiple X1, X2, L, Lxe2x80x2, Ra, Rb, groups in the molecule can be the same or different, and
on the opposite side of the transparent support, an antihalation layer comprising one or more antihalation dyes.
Further, a method of this invention for forming a visible image comprises:
A) imagewise exposing any of the photothermographic materials described above to electromagnetic radiation to form a latent image, and
B) simultaneously or sequentially, heating the exposed photothermographic material to develop the latent image into a visible image.
In some embodiments of this invention to provide an image, any of the photothermographic materials described above has a transparent support and the imaging method of this invention further includes:
C) positioning the exposed and heat-developed photothermographic material with the visible image therein between a source of imaging radiation and an imageable material that is sensitive to the imaging radiation, and
D) thereafter exposing the imageable material to the imaging radiation through the visible image in the exposed and heat-developed photothermographic material to provide a visible image in the imageable material.
In still another embodiment of this invention, a method for preparing a photothermographic emulsion comprises the following steps, in order:
A) providing a photothermographic emulsion comprising silver halide grains and a non-photosensitive source of reducible silver ions, and
B) positioning one or more of the selenium chemical sensitizers represented by Structures I, II, or III noted above, on or around the silver halide grains.
Moreover, another method of preparing a photothermographic emulsion comprises:
A) providing silver halide grains,
B) providing a photothermographic emulsion of the silver halide grains and a non-photosensitive source of reducible silver ions, and
C) during or at any time after step A, chemically sensitizing the silver halide grains with a selenium chemical sensitizer represented by Structures I, II, or III as noted above.
Moreover, another method of preparing a photothermographic emulsion comprises:
A) providing silver halide grains,
B) providing a photothermographic emulsion of the silver halide grains and a non-photosensitive source of reducible silver ions, and
C) during or at any time after step A, chemically sensitizing the silver halide grains with a selenium chemical sensitizer represented by Structures I, II, or III as noted above.
D) during or at any time after step A, chemically sensitizing the silver halide grains by oxidative decomposition of a sulfur-containing compound, or by addition of a sulfur chemical sensitizer, a tellurium chemical sensitizer, a gold chemical sensitizer, or by combinations thereof.
The speed increasing compounds described for use in the phototheimographic materials of this invention have a number of useful properties. For example, they can easily be prepared in good yields as air stable solids and are resistant to hydrolysis. Moreover, they are soluble in a range of useful coating solvents. This allows them to be included easily in the imaging element formulations.
The speed increasing ability of the selenium compounds described herein was not anticipated from the teaching in the prior art. Moreover, prior art chemical sensitizers have generally not produced speed enhancement while maintaining high Dmax and low Dmin.
The photothermographic materials of this invention can be used, for example, in conventional black-and-white or color photothermography, in electronically generated black-and-white or color hardcopy recording. They can be used in microfilm applications, in radiographic imaging (for example, digital medical imaging), and in industrial radiography. Furthermore, the absorbance of these photothermographic materials between 350 and 450 nm is desirably low (less than 0.5) to permit their use in graphic arts (for example, imagesetting and phototypesetting), in the manufacture of printing plates, in contact printing, proofing, and duplicating (xe2x80x9cdupingxe2x80x9d). The photothermographic materials are particularly useful for medical radiography to provide black-and-white images.
In the photothermographic materials of this invention, the components needed for imaging can be in one or more layers. The layer(s) that contain the photosensitive photocatalyst (such as a photosensitive silver halide) or non-photosensitive source of reducible silver ions, or both, are referred to herein as photothermographic emulsion layer(s). The photocatalyst and the non-photosensitive source of reducible silver ions are in catalytic proximity (that is, in reactive association with each other) and preferably are in the same layer. xe2x80x9cCatalytic proximityxe2x80x9d or xe2x80x9creactive associationxe2x80x9d means that they are in the same layer or in adjacent layers.
Various layers are usually disposed on the xe2x80x9cbacksidexe2x80x9d (non-emulsion side) of the materials, including antihalation layer(s), protective layers, antistatic layers, conducting layers, and transport enabling layers.
Various layers are also usually disposed on the xe2x80x9cfrontsidexe2x80x9d or emulsion side of the support, including protective topcoat layers, primer layers, interlayers, opacifying layers, antistatic layers, antihalation layers, acutance layers, auxiliary layers, and others readily apparent to one skilled in the art.
As used herein:
In the descriptions of the photothermographic materials of the present invention, xe2x80x9caxe2x80x9d or xe2x80x9canxe2x80x9d component refers to xe2x80x9cat least onexe2x80x9d of that component. For example, the selenium compounds described herein for chemical sensitization can be used individually or in mixtures.
Heating in a substantially water-free condition as used herein, means heating at a temperature of from about 50xc2x0 C. to about 250xc2x0 C. with little more than ambient water vapor present. The term xe2x80x9csubstantially water-free conditionxe2x80x9d means that the reaction system is approximately in equilibrium with water in the air and water for inducing or promoting the reaction is not particularly or positively supplied from the exterior to the material. Such a condition is described in T. H. James, The Theory of the Photographic Process, Fourth Edition, Eastman Kodak Company, Rochester, N.Y. 1977, p. 374.
xe2x80x9cPhotothermographic material(s)xe2x80x9d means a construction comprising at least one photothermographic emulsion layer or a photothermographic set of layers (wherein the silver halide and the source of reducible silver ions are in one layer and the other essential components or desirable additives are distributed, as desired, in an adjacent coating layer) and any supports, topcoat layers, imagereceiving layers, blocking layers, antihalation layers, or subbing or priming layers. These materials also include multilayer constructions in which one or more imaging components are in different layers, but are in xe2x80x9creactive associationxe2x80x9d so that they readily come into contact with each other during imaging and/or development. For example, one layer can include the non-photosensitive source of reducible silver ions and another layer can include the reducing composition, but the two reactive components are in reactive association with each other.
xe2x80x9cEmulsion layer,xe2x80x9d xe2x80x9cimaging layer,xe2x80x9d or xe2x80x9cphotothermographic emulsion layer,xe2x80x9d means a layer of a photothermographic material that contains the photosensitive silver halide and/or non-photosensitive source of reducible silver ions. It can also mean a layer of the photothermographic material that contains, in addition to the photosensitive silver halide and/or non-photosensitive source of reducible ions, additional essential components and/or desirable additives. These layers are usually on what is known as the xe2x80x9cfrontsidexe2x80x9d of the support.
xe2x80x9cPhotocatalystxe2x80x9d means a photosensitive compound such as silver halide that, upon exposure to radiation, provides a compound that is capable of acting as a catalyst for the subsequent development of the image-forming material.
xe2x80x9cUltraviolet region of the spectrumxe2x80x9d refers to that region of the spectrum less than or equal to 410 nm, and preferably from about 100 nm to about 410 nm, although parts of these ranges may be visible to the naked human eye. More preferably, the ultraviolet region of the spectrum is the region of from about 190 to about 405 nm.
xe2x80x9cVisible region of the spectrumxe2x80x9d refers to that region of the spectrum of from about 400 nm to about 700 nm.
xe2x80x9cShort wavelength visible region of the spectrumxe2x80x9d refers to that region of the spectrum from about 400 nm to about 450 nm.
xe2x80x9cRed region of the spectrumxe2x80x9d refers to that region of the spectrum of from about 600 nm to about 700 nm.
xe2x80x9cInfrared region of the spectrumxe2x80x9d refers to that region of the spectrum of from about 700 nm to about 1400 nm.
xe2x80x9cWon-photosensitivexe2x80x9d means not intentionally light sensitive.
xe2x80x9cTransparentxe2x80x9d means capable of transmitting visible light or imaging radiation without appreciable scattering or absorption.
The sensitometric terms xe2x80x9cphotospeedxe2x80x9d or xe2x80x9cphotographic speedxe2x80x9d (also known as xe2x80x9csensitivityxe2x80x9d), xe2x80x9cabsorbance,xe2x80x9d xe2x80x9ccontrastxe2x80x9d, Dmim, and Dmax have conventional definitions known in the imaging arts. Particularly, Dmin is considered herein as image density achieved when the photothermographic material is thermally developed without prior exposure to radiation.
The sensitometric term absorbance is another term for optical density (OD).
As is well understood in this area, for the selenium compounds defined herein, substitution is not only tolerated, but is often advisable and various substituents are anticipated on the compounds used in the present invention. Thus, when a compound is referred to as xe2x80x9chaving the structurexe2x80x9d of a given formula, any substitution that does not alter the bond structure of the formula or the shown atoms within that structure is included within the formula, unless such substitution is specifically excluded by language (such as xe2x80x9cfree of carboxy-substituted alkylxe2x80x9d). For example, where a benzene ring structure is shown (including fused ring structures), substituent groups may be placed on the benzene ring structure, but the atoms making up the benzene ring structure may not be replaced.
As a means of simplifying the discussion and recitation of certain substituent groups, the term xe2x80x9cgroupxe2x80x9d refers to chemical species that may be substituted as well as those that are not so substituted. Thus, the term xe2x80x9cgroup,xe2x80x9d such as xe2x80x9calkyl groupxe2x80x9d is intended to include not only pure hydrocarbon alkyl chains, such as methyl, ethyl, n-propyl, t-butyl, cyclohexyl, iso-octyl, and octadecyl, but also alkyl chains bearing substituents known in the art, such as hydroxyl, alkoxy, phenyl, halogen atoms (F, Cl, Br, and I), cyano, nitro, amino, and carboxy. For example, alkyl group includes ether and thioether groups (for example, CH3xe2x80x94CH2xe2x80x94CH2xe2x80x94Oxe2x80x94CH2xe2x80x94 and CH3xe2x80x94CH2xe2x80x94CH2xe2x80x94Sxe2x80x94CH2xe2x80x94), haloalkyl, nitroalkyl, alkylcarboxy, carboxyalkyl, carboxamido, hydroxyalkyl, sulfoalkyl, and other groups readily apparent to one skilled in the art. Substituents that adversely react with other active ingredients, such as very strongly electrophilic or oxidizing substituents, would, of course, be excluded by the ordinarily skilled artisan as not being inert or harmless.
In the compounds described herein, no particular double bond geometry (for example, cis or trans) is intended by the structures drawn. Similarly, the alternating single and double bonds and localized charges are drawn as a formalism. In reality, both electron and charge delocalization exists throughout the conjugated chain.
Research Disclosure is a publication of Kenneth Mason Publications Ltd., Dudley House, 12 North Street, Emsworth, Hampshire PO10 7DQ England (also available from Emsworth Design Inc., 147 West 24th Street, New York, N.Y. 10011).
Other aspects, advantages, and benefits of the present invention are apparent from the detailed description, examples, and claims provided in this application.
As noted above, the photothermographic materials of the present invention include one or more photocatalysts in the photothermographic emulsion layer(s). Useful photocatalysts are typically silver halides such as silver bromide, silver iodide, silver chloride, silver bromoiodide, silver chlorobromoiodide, silver chlorobromide and others readily apparent to one skilled in the art. Mixtures of silver halides can also be used in any suitable proportion. Silver bromide and silver bromoiodide are more preferred, with the latter silver halide having up to 10 mol % silver iodide. Typical techniques for preparing and precipitating silver halide grains are described in Research Disclosure, 1978, item 17643.
The shape of the photosensitive silver halide grains used in the present invention is in no way limited. The silver halide grains may have any crystalline habit including, but not limited to, cubic, octahedral, tetrahedral, orthorhombic, rhombic, dodecahedral, other polyhedral, tabular, laminar, twinned, and platelet morphologies, and may have epitaxial growth of crystals thereon. If desired, a mixture of these crystals may be employed. Silver halide grains having cubic and tabular morphology are preferred.
The silver halide grains may have a uniform ratio of halide throughout. They may have a graded halide content, with a continuously varying ratio of, for example, silver bromide and silver iodide or they may be of the core-shell type, having a discrete core of one halide ratio, and a discrete shell of another halide ratio. Core-shell silver halide grains useful in photothermographic materials and methods of preparing these materials are described for example, in U.S. Pat. No. 5,382,504 (Shor et al.), incorporated herein by reference. Iridium and/or copper doped core-shell and non-core-shell grains are described in U.S. Pat. No. 5,434,043 (Zou et al.) and U.S. Pat. No. 5,939,249 (Zou), both incorporated herein by reference.
The photosensitive silver halide can be added to (or formed within) the emulsion layer(s) in any fashion as long as it is placed in catalytic proximity to the non-photosensitive source of reducible silver ions.
It is preferred that the silver halides be preformed and prepared by an ex-situ process. The silver halide grains prepared ex-situ may then be added to and physically mixed with the non-photosensitive source of reducible silver ions. It is more preferable to form the source of reducible silver ions in the presence of ex-situ-prepared silver halide. In this process, the source of reducible silver ions, such as a long chain fatty acid silver carboxylate (commonly referred to as a silver xe2x80x9csoapxe2x80x9d), is formed in the presence of the preformed silver halide grains. Co-precipitation of the reducible source of silver ions in the presence of silver halide provides a more intimate mixture of the two materials [see, for example, U.S. Pat. No. 3,839,049 (Simons)]. Materials of this type are often referred to as xe2x80x9cpreformed soaps.xe2x80x9d
The silver halide grains used in the imaging formulations can vary in average diameter of up to several micrometers (xcexcm) depending on their desired use. Preferred silver halide grains are those having an average particle size of from about 0.01 to about 1.5 xcexcm, more preferred are those having an average particle size of from about 0.03 to about 1.0 xcexcm, and most preferred are those having an average particle size of from about 0.05 to about 0.8 xcexcm. Those of ordinary skill in the art understand that there is a finite lower practical limit for silver halide grains that is partially dependent upon the wavelengths to which the grains are spectrally sensitized. Such a lower limit, for example, is typically from about 0.01 to 0.005 xcexcm.
The average size of the photosensitive doped silver halide grains is expressed by the average diameter if the grains are spherical, and by the average of the diameters of equivalent circles for the projected images if the grains are cubic or in other non-spherical shapes.
Grain size may be determined by any of the methods commonly employed in the art for particle size measurement. Representative methods are described by in xe2x80x9cParticle Size Analysis,xe2x80x9d ASTM Symposium on Light Microscopy, R. P. Loveland, 1955, pp. 94-122, and in C. E. K. Mees and T. H. James, The Theory of the Photographic Process, Third Edition, Macmillan, New York, 1966 Chapter 2. Particle size measurements may be expressed in terms of the projected areas of grains or approximations of their diameters. These will provide reasonably accurate results if the grains of interest are substantially uniform in shape.
Preformed silver halide emulsions used in the material of this invention can be prepared by aqueous or organic processes and can be unwashed or washed to remove soluble salts. In the latter case, the soluble salts can be removed by ultrafiltration, by chill setting and leaching, or by washing the coagulum [for example, by the procedures described in U.S. Pat. No. 2,618,556 (Hewitson et al.), U.S. Pat. No. 2,614,928 (Yutzy et al.), U.S. Pat. No. 2,565,418 (Yackel), U.S. Pat. No. 3,241,969 (Hart et al.) and U.S. Pat. No. 2,489,341 (Waller et al.)].
It is also effective to use an in-situ process in which a halide-containing compound is added to an organic silver salt to partially convert the silver of the organic silver salt to silver halide. The halogen-containing compound can be inorganic (such as zinc bromide or lithium bromide) or organic (such as N-bromosuccinimide).
It is also effective to use mixtures of both preformed and in-situ generated silver halide.
Additional methods of preparing these silver halide and organic silver salts and manners of blending them are described in Research Disclosure, June 1978, item 17029, U.S. Pat. No. 3,700,458 (Lindholm), U.S. Pat. No. 4,076,539 (Ikenoue et al.), and JP Applications 13224/74, 42529/76, and 17216/75.
In some instances, it may be helpful to prepare the photosensitive silver halide grains in the presence of a hydroxytetraazaindene (such as 4-hydroxy-6-methyl-1,3,3,3a,7-tetraazaindene) or an N-heterocyclic compound comprising at least one mercapto group (such as 1-phenyl-5-mercaptotetrazole) to provide increased photospeed. Details of this procedure are provided in copending and commonly assigned U.S. Ser. No. 09/833,533 (filed Apr. 12, 2001 by Shor, Zou, Ulrich, and Simpson), that is incorporated herein by reference.
The one or more light-sensitive silver halides used in the photothermographic materials of the present invention are preferably present in an amount of from about 0.005 to about 0.5 mole, more preferably from about 0.01 to about 0.25 mole, and most preferably from about 0.03 to about 0.15 mole, per mole of non-photosensitive source of reducible silver ions.
The advantages of this invention are provided by chemically sensitizing the silver halide(s) with certain speed increasing selenium compounds. Thus, these selenium compounds can be used effectively as chemical sensitizers.
The advantages of this invention are provided by chemically sensitizing the silver halide(s) with certain speed increasing selenium compounds. Thus, these selenium compounds can be used effectively as chemical sensitizers. They can be represented by the following Structures I, II, or III:
Se(L)m(X1)nxe2x80x83xe2x80x83(I)
M(Lxe2x80x2)s(X2)rxe2x80x83xe2x80x83(II)
xe2x80x83(Z)wMxe2x80x2xSey(CO)zxe2x80x83xe2x80x83(III)
In Structure I, X1 represents a halo (chloro, bromo, or iodo), CN, SCN, SeCN, TeCN, N3, BF4, ClO4, BPh4, PF6, NO3, SO3CF3, O(Cxe2x95x90O)CF3, S(Cxe2x95x90S)N(Ra)(Rb), S(Cxe2x95x90S)ORa, S(Cxe2x95x90S)SRa, S(Pxe2x95x90S)(ORa)(ORb), S(Pxe2x95x90S)(Ra)(Rb), SRa, SeRa, TeRaORa, alkyl (as defined below for Ra and Rb), aryl (as defined below for Ar), or O(Cxe2x95x90O)Ra group wherein Ra and Rb are as defined below. Preferably, X1 represents a halo (such as chloro or bromo), SCN, or S(Cxe2x95x90S)N(Ra)(Rb) group, and more preferably, it represents a halo group such as chloro or bromo. The multiple X1 groups in a Structure I compound can be the same or different groups. Wherever referred to herein, xe2x80x9cPhxe2x80x9d refers to the same or different substituted or unsubstituted phenyl groups.
The xe2x80x9cRa and Rbxe2x80x9d groups used to define substituent groups in X1 can be any suitable substituted or unsubstituted alkyl group having 1 to 20 carbon atoms (including all possible isomers, such as methyl, ethyl, isopropyl, t-butyl, octyl, decyl, trimethylsilylmethyl, and 3-trimethylsilyl-n-propyl), substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms (including all possible isomers such as ethenyl, 1-propenyl, and 2-propenyl) or substituted or unsubstituted carbocyclyl groups (such as cyclopentyl, cyclohexyl, or cycloheptyl), heterocyclyl groups (such as morpholinyl, piperidyl, and piperazyl), or aryl group (Ar) having 6 to 10 carbon atoms in the single- or fused-ring system (such as phenyl, 4-methylphenyl, anthryl, naphthyl, xylyl, mesityl, indenyl, pentafluorophenyl, 2,4,6-tri(t-butyl)phenyl, p-methoxyphenyl, 3,5-dimethylphenyl, p-tolyl, pyridyl, and 2-phenylethyl). In addition, when X1 groups contain more than an Ra and an Rb group, these groups may be joined together to form a substituted or unsubstituted 5- to 7-membered heterocyclic ring. Preferably, Ra and Rb are a substituted or unsubstituted alkyl group having 1 to 8 carbon atoms, or a substituted or unsubstituted phenyl group. Unless otherwise noted, multiple Ra and Rb, groups in a molecule can be the same or different groups.
L represents the same or different neutral Lewis base ligands, such as ligands derived from thiourea, substituted thioureas, cyclic thioureas such as imidazolidine-2-thione, substituted cyclic thioureas such as N,N-dimethyl-imidazolidine-2-thione, pyridine, and substituted pyridines. Preferably, L is a ligand derived from thiourea or a substituted thiourea, and more preferably, it is a ligand derived from a substituted thiourea as defined below in Structures IV, V, or VI. Multiple L groups in the Structure I groups can be the same or different groups.
Also in Structure I, m is 0, 1, 2, 3, or 4 and n is 2 or 4. However, when m is 0, n is 2 or 4, and when m is 0 and n is 2, then X1 is not Ra, Rb, or RaSe. Preferably, m is 2 and n is 2 or 4. More preferably, m is 0 and n is 2. Even more preferably, m is 0, n is 2 and X is a 1,1-dithio containing anionic ligand such as S(Cxe2x95x90S)N(Ra)(Rb), S(Cxe2x95x90S)ORa, S(Cxe2x95x90S)SRa, S(Pxe2x95x90S)(ORa)(ORb), S(Pxe2x95x90S)(Ra)(Rb).
In Structure II, M represents Pd, Pt, or Cu. X2 represents a halo (chloro, bromo, or iodo), CN, SCN, SeCN, TeCN, N3, BF4, ClO4, BPh4, PF6, NO3, SO3CF3, O(Cxe2x95x90O)CF3, S(Cxe2x95x90S)N(Ra)(Rb), S(Cxe2x95x90S)ORa, S(Cxe2x95x90S)SRa, S(Pxe2x95x90S)(ORa)(ORb), S(Pxe2x95x90S)(Ra)(Rb), SRa, SeRa, TeRaORa, alkyl (as defined above for Ra and Rb), aryl (as defined above for Ar), or O2CRa group in which Ra and Rb are as defined above. Preferably, X2 represents a halo, SCN, or SeCN group. More preferably, X2 represents a chloro, bromo, or SCN group. The multiple X2 groups in Structure II compounds can be the same or different groups.
Lxe2x80x2 represents a neutral ligand with a Group 15 atom (that is, N, P, As, Sb, or Bi) or a Group 16 atom (that is, S, Se, Te). Useful neutral ligands incorporating Group 15 atoms include pyridine, bipyridine, thiourea, substituted thioureas, selenourea, substituted selenoureas, and organophosphines such as P(Ra)(Rb)(Rc). Lxe2x80x2 also includes ligands of the type E(Ra)(Ra)(Rc) where E represents N, As, Sb, Bi, and Ra and Rb are as defined above, and Rc is alkyl or aryl as defined above for Ra and Rb. Lxe2x80x2 also includes chalcogen ligands of the type Exe2x80x2xe2x95x90P(Ra)(Rb)(Rc) where Exe2x80x2 represents S, Se, and Te and Ra, Rb, and Rc are as defined above. However, at least one of Lxe2x80x2 or X2 must contain a selenium atom.
Examples of ligands of the type Exe2x95x90P(Ra)(Rb)(Rc) include, for example, Sxe2x95x90P(C6H5)3, Sexe2x95x90P(C6H5)3, Texe2x95x90P(i-C3H7)3, Sexe2x95x90P(C6H11)3, Sexe2x95x90P(p-CF3xe2x80x94C6H4)3, Sexe2x95x90P(p-CH3Oxe2x80x94C6H4)3, and Sexe2x95x90P(C6F,)(C6H5)2. Suitable phosphine tellurides have been described in, R. A. Zingaro et al., J. Organometal. Chem., 1965, 4, 320. Suitable organophosphine sulfides and selenides have been described in J. A. Miller, Organophosphorus Chem., 1976, 4, 66-77 and in T. S. Lobana, Organophosphorus Compd., Vol. 4, pp. 409-566, Wiley, NY, 1996.
Also in Structure II, when M represents Pd(2+) or Pt(2+), r is 2 and s is 1, 2, 3, or 4. When M represents Cu(1+), r is 1 and s is 1, 2, 3, or 4.
In Structure III, Z represents a monovalent cation such as Li+, Na+, K+, Rb+, Cs+, (Ra)4N+, (Ra)4P+, [P(Ra)3]2N+, Mxe2x80x2 represents Fe, Ru, Os, Co, Rh, or Ir, x is an integer of from 1 to 6, y is an integer of from 1 through 6, z is an integer of from 6 through 20, w is an integer inclusive of 0 through 4 and represents the number of Z groups necessary to neutralize the electronic charge on the rest of the molecule, and Ra is as defined above.
In a preferred embodiment of Structure I compounds, when m is 0 and n is 2 or 4, the compounds represented by Structure I can be further represented by Structure I-a, 
In Structure I-a, X represents the same or different CORa, CSRa, CN(Ra)(Rb), CRa, P(Ra)(Rb) or P(ORa)(ORb) group that is attached to the two sulfur atoms through the noted carbon or phosphorus atom in the groups. Preferably, X represents the same or different CORa, CSRa or CN(Ra)(Rb), P(Ra)(Rb) or P(ORa)(ORb) group. Also in Structure I-a, p is 2 or 4, and preferably it is 2. Thus, when p is 2 (as noted below), there can be 2 of the same or 2 different X groups. When p is 4, there can be 4 of the same X groups, or 2, 3, or 4 different X groups in the molecule.
Unless otherwise noted, the multiple Ra and Rb groups in the Structure III compounds can be the same or different groups. However, in some embodiments, when p is 2, X cannot be two identical CN(Ra)(Rb) groups.
In Structures I and II, preferred thiourea ligands are derived from compounds represented below by Structures IV, V, or VI: 
In Structure IV, R1, R2, R3, and R4 independently represent hydrogen, substituted or unsubstituted alkyl groups (including alkylenearyl groups such as benzyl), substituted or unsubstituted alyl groups (including arylenealkyl groups), substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted alkynyl groups and heterocyclic groups.
Useful alkyl groups are branched or linear and can have from 1 to 20 carbon atoms (preferably having 1 to 5 carbon atoms), useful aryl groups can have from 6 to 14 carbon atoms in the carbocyclic ring, useful cycloalkyl groups can have from 5 to 14 carbon atoms in the central ring system, useful alkenyl and alkynyl groups can be branched or linear and have 2 to 20 carbon atoms, and useful heterocyclic groups can have 5 to 10 carbon, oxygen, sulfur and nitrogen atoms in the central ring system (they can also have fused rings).
These various monovalent groups can be further substituted with one or more groups including but not limited to, halo groups, alkoxycarbonyl groups, hydroxy groups, alkoxy groups, cyano groups, acyl groups, acyloxy groups, carbonyloxy ester groups, sulfonic acid ester groups, alkylthio groups, dialkylamino groups, carboxy groups, sulfo groups, phosphono groups, and any other group readily apparent to one skilled in the art. R1, R2, R3, and R4 can independently be alkyl groups.
Alternatively, R1 and R3 taken together, R2 and R4 taken together, R1 and R2 taken together, or R3 and R4 taken together, can form a substituted or unsubstituted 5- to 7-membered heterocyclic ring.
Where R1 and R3 are taken together or R2 and R4 are taken together, the heterocyclic rings can be saturated or unsaturated and can contain oxygen, nitrogen or sulfur atoms in addition to carbon atoms. Useful rings of this type include, but are not limited to, imidazole, pyrroline, pyrrolidine, thiohydantoin, pyridone, morpholine, piperazine and thiomorpholine rings. These rings can be substituted with one or more alkyl groups (having 1 to 5 carbon atoms), aryl groups (having 6 to 10 carbon atoms in the central ring system), cycloalkyl groups (having 5 to 10 carbon atoms in the central ring system), alkoxy groups, carbonyloxyester groups, halo groups, cyano groups, hydroxy groups, acyl groups, alkoxycarbonyl groups, sulfonic ester groups, alkylthio groups, carbonyl groups, carboxy groups, sulfo groups, phosphono groups, and other groups readily apparent to one skilled in the art.
Where R1 and R2 are taken together or R3 and R4 are taken together, the heterocyclic rings can be saturated or unsaturated and can contain oxygen, nitrogen or sulfur atoms in addition to carbon atoms. Useful rings of this type include, but are not limited to, 2-imidazolidinethione, 2-thioxo-1-imidazolidinone (thiohydantoin), 1,3-dihydro-2H-imidazole-2-thione, 1,3-dihydro-2H-benzimidazole-2-thione, tetrahydro-2,2-thioxo-5-pyrimidine, tetrahydro-1,3,5,-triazine-2(1H)-thione, dihydro-2-thioxo-4,6-(1H,3H)-pyrimidinedione, dihydro-1,3,5-triazine-2,4-(1H,3H)-dione and hexahydrodiazepine-2-thione rings. These rings can be substituted with one or more alkyl groups (having 1 to 5 carbon atoms), aryl groups (having 6 to 10 carbon atoms in the central ring system), cycloalkyl groups (having 5 to 10 carbon atoms in the central ring system), carbonyloxyester groups, halo groups, cyano groups, hydroxy groups, acyl groups, alkoxycarbonyl groups, sulfonic ester groups, alkylthio groups, carbonyl groups, alkoxy groups, carboxy groups, sulfo groups, phosphono groups, and other groups readily apparent to one skilled in the art.
Preferably, R1, R2, R3, and R4 independently represent hydrogen, alkyl, alkenyl, alkynyl, aryl, and heterocyclic groups, more preferably hydrogen, alkyl, aryl, and alkenyl groups, and most preferably alkenyl groups. A preferred alkenyl group is an allyl group. A preferred alkyl group is a methyl group.
In Structure V noted above, R1, R2, R3, R4 and R5 have the same definitions as noted above for R1, R2, R3 and R4 in Structure IV with the following differences:
R1 and R3 can be taken together, R2 and R4 can be taken together, R3 and R5 can be taken together and/or R4 and R5 can be taken together, to form substituted or unsubstituted 5- to 7-membered heterocyclic rings (as described above for Structure IV). When those heterocyclic rings are formed from R1 and R3 taken together or R2 and R4 taken together, they are as defined above for R1 and R3 taken together for Structure IV, but the resulting heterocyclic rings can have other substituents such as alkoxy groups, dialkylamino groups, and carboxy, sulfo, phosphono and other acidic groups. When those heterocyclic rings are formed from R3 and R5 taken together or R4 and R5 taken together, they can be substituted as described for R1 and R3 of Structure IV Useful rings of this type include, but are not limited to, 2-imidazolidinethione, 2-thioxo-1-imidazolidinone (thiohydantoin), 1,3-dihydro-2H-imidazole-2-thione, 1,3-dihydro-2H-benzimidazole-2-thione, tetrahydro-2,2-thioxo-5-pyrimidine, tetrahydro-1,3,5,-triazine-2(1H)-thione, dihydro-2-thioxo-4,6-(1H,3H)-pyrimidinedione, dihydro-1,3,5-triazine-2,4-(1H,3H)-dione and hexahydrodiazepine-2-thione rings.
For Structure V, the preferred groups for R1-R5 are hydrogen, alkyl, alkenyl, alkynyl, aryl, and heterocyclic groups, more preferably alkyl, aryl, and alkenyl groups, and more preferably alkenyl groups. A preferred alkenyl group is an allyl group.
Also in Structure V, most preferable alkyl groups are methyl and ethyl groups. Most preferable aryl groups are phenyl or tolyl groups. Most preferable cycloalkyl groups are cyclopentyl and cyclohexyl groups. Most preferably the alkenyl group is an allyl group. Most preferable heterocyclic groups are morpholino and piperazino groups.
In Structure VI noted above, R1, R2, R3, R4, R5, and R6 have the same definitions as noted above for R1, R2, R3, R4, and R6 in Structure V described above. In addition, R3 and R5 taken together, R4 and R5 taken together, R1 and R3 taken together, R2 and R4 taken together, or R5 and R6 taken together, can form a substituted or unsubstituted 5- to 7-membered heterocyclic ring as described above for the heterocyclic rings in Structure V.
R7 is a divalent aliphatic or alicyclic linking group including but not limited to substituted or unsubstituted alkylene groups having 1 to 12 carbon atoms, substituted or unsubstituted cycloalkylene groups having 5 to 8 carbon atoms in the ring structure, substituted or unsubstituted arylene groups having 6 to 10 carbon atoms in the ring structure, substituted or unsubstituted divalent heterocyclyl groups having 5 to 10 carbon, nitrogen, oxygen, and sulfur atoms in the ring structure, or any combination of two or more of these divalent groups, or any two or more of these groups connected by ether, thioether, carbonyl, carbonamido, sulfoamido, amino, imido, thiocarbonyl, thioamido, sulfinyl, sulfonyl, or phosphinyl groups. Preferably, R7 is a substituted or unsubstituted alkylene group having at least 2 carbon atoms.
Further details of these preferred thiourea ligands are provided in copending and commonly assigned U.S. Ser. No. 09/667,748 filed Sep. 21, 2000 by Lynch, Simpson, Shor, Willett, and Zou, incorporated herein by reference. Most preferably, the thiourea compounds are substituted with the same aliphatic substituent.
Representative selenium chemical sensitizers of Structures I, II, or III include, but are not limited to, the following compounds. It is to be understood that in coordination compounds, the exact chemical structures may not be known. The structures shown below are representative of the stoichiometry of the selenium compounds. xe2x80x83Pd[Se(p-anisyl)2]2Br2xe2x80x83xe2x80x83II-1
Pd[Se(mesityl)2]2Cl2xe2x80x83xe2x80x83II-2
Pd{Se[CH2Si(CH3)3]2}2(SCN)2xe2x80x83xe2x80x83II-3
Pd[P(p-CH3Oxe2x80x94C6H4)3]2[SeCN]2xe2x80x83xe2x80x83II-4
Pd[P(C6H5)3]2[SeCN]2xe2x80x83xe2x80x83II-5
Cu[P(p-CH3Oxe2x80x94C6H4)3]3SeCNxe2x80x83xe2x80x83II-6
xe2x80x83Pt[Se(p-CH3xe2x80x94C6H4)2]2[SeC6H5]2xe2x80x83xe2x80x83II-7
Pt[P(p-CH3Oxe2x80x94C6H4)3]2[SeCN]2xe2x80x83xe2x80x83II-8
[Pt{Sexe2x95x90C(NH2)(NMe2)}4]Br2xe2x80x83xe2x80x83II-9
Cu[P(C6H5)3]2SeCNxe2x80x83xe2x80x83II-10
Cu[P(C6H5)3]3SeCNxe2x80x83xe2x80x83II-11
Cu[Se(Mesityl)2]2Brxe2x80x83xe2x80x83II-12
Cu[(C6H5)2PCH2CH2P(C6H5)2]SeCNxe2x80x83xe2x80x83II-13
Cu[Se(CH2xe2x80x94C6H5)2]3SeCNxe2x80x83xe2x80x83II-14
Cu[P(p-CH3xe2x80x94C6H4)3]2SeC6H5xe2x80x83xe2x80x83II-15
Cu{CH3C[CH2P(C6H5)2]3}SeCNxe2x80x83xe2x80x83II-16
xe2x80x83[Cu{Sexe2x95x90C(NH2)(NMe2)}3]BF4xe2x80x83xe2x80x83II-17
Cu[Se(C6H5)2]3SeCNxe2x80x83xe2x80x83II-18
Pd[As(C6H5)3]2(SeCN)2xe2x80x83xe2x80x83II-19
Pd(C5H4N)2(SeCN)2xe2x80x83xe2x80x83II-20
Pt[Sb(p-CH3xe2x80x94C6H4)3]2(SeCN)2xe2x80x83xe2x80x83II-21
Cu[Se(2xe2x80x94C5H4N)2](SeC6H5)xe2x80x83xe2x80x83II-22
Cu[P(p-CH3xe2x80x94C6H4)3]2SeCNxe2x80x83xe2x80x83II-23
Cu[Se(C6H5)2]3SeC6H5xe2x80x83xe2x80x83II-24
Pd[(CH3)2N(Sexe2x95x90C)NE2]2(SeCN)2xe2x80x83xe2x80x83II-25
Cu[P(C6H5)3]SeCNxe2x80x83xe2x80x83II-26
xe2x80x83Cu[Se(C6H5)2]4BF4xe2x80x83xe2x80x83II-27
Pt[Se(C6H5)2]2(SeCN)2xe2x80x83xe2x80x83II-28
Pt[Se(C6H5)2]4(PF6)2xe2x80x83xe2x80x83II-29
Pt[H2N(Sexe2x95x90C)NH2]4(BF4)2xe2x80x83xe2x80x83II-30
Pt[CH3C(CH2P(C6H5)2]3(SeCN)(PF6)xe2x80x83xe2x80x83II-31
Pd[Se(C6H5)2]3(SeC6H5)(BF4)xe2x80x83xe2x80x83II-32
Fe3(xcexc3-Se)2(CO)9xe2x80x83xe2x80x83III-1
Fe4Se4(CO)12xe2x80x83xe2x80x83III-2
Ru3Se2(CO)9xe2x80x83xe2x80x83III-3
RuCo2Se(CO)9xe2x80x83xe2x80x83III-4
xe2x80x83Os3Se2(CO)9xe2x80x83xe2x80x83III-5
Ru4Se4(CO)12xe2x80x83xe2x80x83III-6
[(CH3)4N][Rh3Se2(CO)6]xe2x80x83xe2x80x83III-7
The selenium chemical sensitizers described herein by Structures I, II, and III can be used individually or in mixtures. They can be present in one or more imaging layer(s) on the front side of the photothermographic material. Preferably, they are in every layer that contains the photocatalyst (for example, photosensitive silver halide). The total amount of such compounds in the material will generally vary depending upon the average size of silver halide grains. The total amount is generally at least 10xe2x88x927 mole per mole of total silver, and preferably from about 10xe2x88x925 to about 10xe2x88x922 mole per mole of total silver for silver halide grains having an average size of from about 0.01 to about 2 xcexcm. The upper limit can vary depending upon the compound used, the level of silver halide and the average grain size, and it would be readily determinable by one of ordinary skill in the art.
The selenium chemical sensitizers useful in the present invention can be prepared using readily available starting materials and known procedures as well as the procedures detailed in the Synthetic Examples below. The Se(2+) coordination complexes with thiourea and substituted thiourea ligands (for example, [Se(L)2(X1)2] and [Se(L)4](X1)2, where X1 is Cl or Br, and L is a thiourea or a substituted thiourea ligand) can be most conveniently prepared by reacting a solution of a Se(4+) compound, typically a salt of [Se(Xxe2x80x2)6]2xe2x88x92, with a thiourea ligand in an appropriate stoichiometry to give the di- or tetra-thiourea-selenium product. In these reactions the thiourea derivative functions both as the reducing agent for the Se(4+) to Se(2+) reduction, as well as a stabilizing ligand for the Se(2+) product.
Once prepared, compounds such as, for example, [Se(thiourea)2Cl2], can be used to prepare a wide variety of related derivatives such as, for example, [Se(thiourea)2(X1)2] (where X1 is an anionic ligand such as a pseudohalide) by substitution reactions using an appropriate salt of the anion (X1)xe2x88x92 for example, K[SCN]. Examples of such syntheses can be found in S. V. Bjxc3x8rnev{dot over (a)}g and S. Hauge, Acta. Chem. Scand., 1983, 37A, 235-240, S. Hauge and M. Tysseland, Acta Chem. Scand. 1971, 25, 3072-3080, O Vikane, Acta Chem. Scand., 1975, 29A, 763-770, O. Vikane, Acta Chem. Scand., 1975, 29A, 787-793, S. Sowrirajan, G. Aravamudan, M. Seshasayee, and G. C. Rout, Acta Cryst., 1985, 41C, 576-579, K. J. Wynne, P. S. Pearson, M. G. Newton, and J. Golen, Inorg. Chem., 1972, 11, 1192-1196.
Selenium(2+) complexes of the type Se(thiourea)(Aryl)X1, where X1 is, for example, Cl, Br, I, or SCN can be prepared by reaction of a diaryldiselenide with a thiourea and halogen (for example, Cl2 or Br2). These reactions are typically carried out in methanol. When such reactions are carried out using excess thiourea, derivatives of the type Se(thiourea)2(Aryl)Cl can be prepared. Synthetic procedures for such mixed organometallic complexes have been described in the literature. Examples of such syntheses can be found in, for example, S. Hauge, Ø. Johnnesen, and O. Vikane, Acta Chem. Scand., 1978, 32A, 901, O. Vikane, Acta Chem. Scand., 1975, 29A, 763, O. Vikane, Acta Chem. Scand., 1975, 29A, 787, and O. Vikane, Acta Chem. Scand., 1975, 29A, 150.
Selenium(2+) coordination complexes with 1,1-dithio ligands such as, for example those described in Structure I-a where p is 2, and X is, for example, CN(Ra)2, CORa, P(Ra)2, P(ORa)2, or C(Ra) can be prepared by the addition of 2 equivalents of a water soluble salt of the 1,1-dithio anion (typically an alkali metal or ammonium salt, for example, Na[S2X]) to an aqueous solution of the labile Se(2+) thiosulfate complex, Na2[Se(S2O3)2].3H2O (prepared as described in O. Foss, Inorganic Syntheses, 1953, 4, 88). The products, of such substitution reactions, [Se(S2X)2], readily precipitate from the aqueous reaction solution, and after isolation by filtration, washing well with water, and vacuum or air drying, they can be recrystallized from organic solvents. Typical procedures for preparing such [Se(S2X)2] type complexes have been reported in the literature. Compounds such as [Se(S2CNEt2)2], [Se(S2CNMe2)2], [Se(S2COMe)2], and [Se(S2COEt)2] have been prepared as described in O. Foss, Inorganic Syntheses, 1953, 4, 91-93. [Se{S2CN(CH2)4O}2] has been prepared as described in O. P. Anderson and S. Husebye, Acta Chem. Scand., 1970, 24, 3141. [Se {S2P(OMe)2}2], [Se {S2P(OEt)2}2], and [Se {S2PEt2}2] have been prepared as described in S. Husebye, Acta Chem. Scand., 1965, 19, 1045.
Complexes of this type can be prepared more conveniently in a 1-step procedure in which the labile Se(2+) thiosulfate complex, Na2[Se(S2O3)2] is prepared in-situ at low temperature (typically xe2x88x925xc2x0 C. to 0xc2x0 C.) and immediately reacted with 2 equivalents of the appropriate 1,1-dithio salt. Synthetic Examples 1 and 2 detail the use of this synthetic procedure to prepare [Se(S2CNEt2)2] and [Se{S2P(OEt)2}2]. The analogous Se(2+) complex with the 1,3-dithio ligand, [Ph2P(S)NP(S)Ph2](1xe2x88x92) (that is, [Se{Ph2P(S)NP(S)Ph2xe2x80x94S,Sxe2x80x2}2]) can be prepared by reaction of [Se{S2P(OEt)2}2] with 2 equivalents of NH4[Ph2P(S)NP(S)Ph2] in methanol solution as described in S. Husebye and K. Martmann-Moe, Acta. Chem. Scand., 1983, 37A, 219-225.